Light Ray Based Calibration System and Method

ABSTRACT

The present disclosure relates to a system and method for calibrating an optical device, such as a camera. In one example, the system includes a light-emitting device that generates light patterns and an ray generator that is positioned between the light-emitting device and the optical device. The ray generator separates the light emitted as part of the light patterns into a plurality of directional rays. The optical device then captures the directional rays and the captured data, along with data corresponding to the light pattern and the ray generator, are used to calibrate the optical device.

TECHNICAL FIELD

The technology described herein relates generally to methods and systemsfor calibrating optical devices.

BACKGROUND

Many applications, such as measurement systems, require that the lensproperties of cameras are calibrated. Certain lens properties can affectthe accuracy of images captured by a camera and can be difficult todetect. Accurate images captured by a camera can be used to calibrateother devices such as projectors, track objects, determine depth ofobjects, image stitching, three dimensional reconstruction, and so on.Given that the accuracy of the camera images are required in order tohave accurate data entry into the other uses for the images, cameras areoften required to be calibrated before use.

Conventional calibration methods are typically time intensive,cumbersome, and/or require specialized calibration hardware and softwaretools. One conventional calibration method requires a planar checkboardthat is moved around by a user to different spatial locations around thecamera. The user then captures images of the checkboard in the differentlocations and this information is used to determine the lens propertiesof the camera. While this technique can generate acceptable calibrationresults, it depends heavily on the experience of the user, is very timeintensive, and requires a large amount of space in order to accuratelycalibrate the various lens properties of the camera.

SUMMARY

One example of the present disclosure relates to a system and method forcalibrating an optical device, such as a camera. In one example, thesystem includes a light-emitting device or a light source that emitslights and an ray generator positioned between the light-emitting deviceand the optical device. The ray generator separates the emitted lightinto a plurality of directional rays. The optical device then capturesthe directional rays and the captured data, along with datacorresponding to the emitted light and the ray generator, which are usedto calibrate the optical device. The ray generator may be an maskingelement, such as an optical mask, one or more lenses, a diffractiongrating or substantially any device that can define or create thedirectional rays.

Another example of the present disclosure relates generally to a methodfor calibrating an optical device. The method includes generating by thelight-generating device a light pattern, separating by an ray generatorthe light pattern into a plurality of light rays, capturing one or moreimages by the optical device of the plurality of light rays, anddetermining by a processing element one or more lens properties of theoptical device based on the light ray images captured by the opticaldevice.

Yet another example of the present disclosure includes a calibrationassembly for use in calibrating a camera. The calibration assemblyincludes an emitting device that generates light wavelengths and an raygenerator in optical communication with the emitting device. Inoperation, the ray generator separates the light wavelengths emittedfrom the emitting device into one or more directional light rays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a calibration system.

FIG. 2 is a simplified block diagram of a computer of the calibrationsystem of FIG. 1.

FIG. 3 is an isometric view of a first example of a calibration assemblyincluding an emitting device and an ray generator.

FIG. 4 is a partially exploded view of the calibration assembly of FIG.3.

FIG. 5 is an enlarged view of the ray generator of calibration assemblyof FIG. 4.

FIG. 6 is a partially exploded view of a second example of a calibrationassembly.

FIG. 7 is an enlarged view of a wavelength specific ray generator of thecalibration assembly of FIG. 6.

FIG. 8 is an isometric view of the calibration assembly of FIG. 6aligned with an optical device for calibration.

FIG. 9 is a flow chart illustrating a method for calibrating an opticaldevice using the calibration system of FIG. 1.

FIG. 10 is a side elevation view of the calibration assembly integratedinto an attachable module that connects directly to the optical device.

SPECIFICATION

The present disclosure is generally related to a system and method forcalibrating optical devices, such as cameras. The system simulates pointpatterns in space to generate hallucinations of light points, and usesthe simulated points to calibrate an optical device. In one embodiment,the system includes a light-emitting device, such as an electronicvisual display (e.g., liquid crystal display, plasma display, etc.) andone or more ray generators for generating directional light rays. Tocalibrate an optical device, different light patterns are generated bythe emitting device, separated by the ray generator into directionallycoded light rays, and an image of the rays is captured by the opticaldevice. The light ray patterns generated by the emitting device, alongwith the known information of the ray generator, can then be used todetermine different characteristics of the optical device based on thecaptured images.

As used herein, the term directional ray is meant to encompassdirectionally coded light rays.

The ray generator can be passive, such as a static opaque layer withmultiple ray apertures defined in various locations across the layer.Alternatively, the ray generator can be active and dynamically generateray apertures in different locations, such as a liquid crystal displayhaving pixels that can be activated to pass or block light.Additionally, the ray generators can also be color specific to generateadditional directional rays. For example, the ray generator may includemultiple layers that allow only certain wavelengths to pass through themain body, e.g., cyan, magenta, and yellow layers can be used topartially block red, green, and blue light. In these embodiments, theray apertures define the singular pathway for light of the blockedcolor. By stacking the color blocking layers, or otherwise arrangingthem in different orders and distances between the emitting device, theaccuracy of the calibration process can be improved and can be completedfaster due to the increased amount of data with each captured image.Further, in these embodiments, the camera can be calibrated on aspectral basis to account for instances where the camera lens mayrefract different light wavelengths differently. In these instances, thecalibration process allows the lens properties to be calibrated for red,green, and blue (or different wavelengths) individually.

An example of a calibration system 100 is shown in FIG. 1. Withreference to FIG. 1, the calibration system 100 includes a computer 102,a light-emitting device 103 or light source, an ray generator 104, andan optical device 106. The system 100 can be used to calibrate a numberof optical devices, but in one embodiment, the optical device 106 is adigital camera having a lens and an image sensor. In some embodiments,the light-emitting device 103 and ray generator 104 form the calibrationassembly and data captured by the optical device 106 from use with thecalibration assembly is input into the computer 102 for calibrating theoptical device.

The light-emitting device 103 or light source generates incident light(e.g., light wavefront) that is captured by the optical device 106. Thelight-emitting device 103 or emitter can be tailored to generate and/oremit light wavelengths. In one embodiment, the light-emitting device 103is an electronic visual display screen, such as a liquid crystal display(LCD). Other examples of emitting devices 103 include plasma displays,light-emitting diode (LED) display, organic light-emitting display,field emission display, laser display, a plurality of laser lightsources, or the like. The emitting device 103 is typically configured toemit spatially controllable light and often may require a pixel densitysufficient to achieve a desired calibration for the camera. For example,the higher the pixel density the more accurate the calibration, but asthe pixel density is increased the pixel size may be reduced, whichreduces the light emitted from each pixel, such that the calibration maytake longer to get the same amount of photons as compared to largerpixels. Accordingly, the pixel density can be selected based on atradeoff of the calibration accuracy and calibration time.

The computer 102 is used to process image data from the optical device106, as well as light ray information from the ray generator 104 and/orlight-emitting device 103. FIG. 2 is simplified block diagram of thecomputer 102. It should be noted that although in the example of FIG. 1,only one computer 102 is shown; however, in other embodiments, more thanone computer or server may be used. The computer 102 may include one ormore processing elements 108, a network interface 110, a power source114, a display 120, one or more memory components 116, and aninput/output (I/O) interface 112. Each of the elements of the computer102 may be in communication via one or more system buses, wirelessly, orthe like.

The processing element 108 is any type of electronic device capable ofprocessing, receiving, and/or transmitting instructions. For example,the processing element 108 may be a microprocessor or microcontroller.Additionally, it should be noted that select components of the computer102 may be controlled by a first processor and other components may becontrolled by a second processor, where the first and second processorsmay or may not be in communication with each other.

The memory 116 stores data used by the computer 102 to storeinstructions for the processing element 108, as well as storeoptimization, calibration, and other camera 106 and ray generator 104data for the calibration system 100. For example, the memory 116 maystore data or content, such as, but not limited to, audio files, videofiles, and so on, corresponding to various applications. The memory 116may be, for example, magneto-optical storage, read-only memory, randomaccess memory, erasable programmable memory, flash memory, or acombination of one or more types of memory components.

A power source 114 provides power to the components of the computer 102and may be a battery, power cord, or other element configured totransmit power to the computer 102.

The display 120 provides visual feedback to a user and, optionally, canact as an input element to enable a user to control, manipulate, andcalibrate various components of the calibration system 100. The display120 may be similar to the light emitter 103 and be any suitable display,such as a liquid crystal display, plasma display, organic light-emittingdiode display, and/or cathode ray tube display. In embodiments where thedisplay 120 is used as an input, the display may include one or moretouch or input sensors, such as capacitive touch sensors, resistivegrid, or the like.

The I/O interface 112 allows a user to enter data into the computer 102,as well as provides an input/output for the computer 102 to communicatewith other devices (e.g., camera 106, light-emitting display 103, raygenerator 104, other computers, speakers, etc.). The I/O interface 112can include one or more input buttons, touch pads, and so on.

The network interface 110 provides communication to and from thelight-emitting device 103, the ray generator 104, and/or the camera 106,and the computer 102. The network interface 110 includes one or morecommunication protocols, such as, but not limited to WiFi, Ethernet,Bluetooth, and so on.

The ray generator 104 is used to generate directional or angled lightrays. In some embodiments, the ray generator 104 defines an optical maskand includes a light blocking substrate that includes one or more rayapertures. In these embodiments, the light blocking aspect of the raygenerator blocks, absorbs, and/or reflects the incident light. The rayapertures allow light to pass through the ray generator and may bepermanently defined, such as holes cut into the material, or may bevariable, such as pixels in an LCD that selectively allow light through.In the latter example, the ray apertures can be dynamically modified tovary the angle of the light rays that are transmitted therethrough. Inother embodiments, the ray generator 104 may generate the rays in othermanners. For example, in one embodiment, the ray generator may be adiffraction grating or a plurality of small lenses (e.g., lenslet array)that are used with a corresponding light source to generate directionalrays. In the first example, the diffraction grating can be used with oneor more laser light sources to create or define the directional rays.

Depending on the embodiment, the ray generator 104 may be one or morelayers and is typically configured to correspond to the shape anddimensions of the emitting device 103. The ray generator 104 may becurved to further modify the ray generation or may be spaced atdifferent distances from the emitting device 103 as discussed below. Inexamples where an active ray generator is used, the generator mayoptionally block colored wavelengths or select wavelengths, rather thanall wavelengths. The ray generator 104 can be integrated with theemitting device 103 (i.e., be the same device, such as a holographicdevice that hallucinates virtual 3D points) or may be separate from theemitting device 103. The ray generator 104 acts as a parallax barrierdevice that in effect generates a holographic light pattern that can becaptured by the optical device.

A first example of the ray generator 104 is shown in FIGS. 3-5. Withreference to FIGS. 3 and 4, in this example, the ray generator 104defines an optical mask and is a perforated plane or substrate placeddirectly on top of the light-emitting device 103, which in thisembodiment is an LCD screen for a portable electronic device. The raygenerator 104 is positioned within or formed integrally with a spacinglayer 130. The spacing layer 130 sets a fixed, predetermined distance,between the light-emitting device 103 and the ray generator 104. In oneembodiment, the spacing layer 130 is a clear glass or other transparentcomponent that transmits all wavelengths therethrough. However, in otherembodiments, the spacing layer 130 may form a portion of the raygenerator 104 and may block select wavelengths.

The spacing layer 130 may have a width that determines the spacingdistance between the ray generator 104 and the light-emitting device103, e.g., the width of the spacing layer 130 is the spacing distanceand the ray generator 104 engages the top surface of the spacing layer130 and the light-emitting device 103 engages the bottom surface of thespacing layer 130. In other embodiments, the spacing layer 130 may beheld at a predetermined distance, e.g., by spacing elements such asblocks, rubber elements, or the like. The spacing layer 130 may beselected to have the substantially the same dimensions as thelight-emitting device 103 or the dimensions may be selected based on adesired light-emitting region and may block light from the emittingdevice 103 that falls outside of the desired region.

With reference to FIG. 5, in this embodiment, the ray generator 104includes a blocking substrate 136 that blocks one or more lightwavelengths from passing therethrough. The blocking substrate 136 may beselected to block or mask all wavelengths and be completely opaque ormay allow select wavelengths to pass therethrough. A plurality of rayapertures 134 are defined throughout the blocking substrate 136 andallow light from the light-emitting device 103 and the spacing layer 130to be transmitted therethrough. In one example, the ray apertures 134are generated by a laser that creates the apertures through thesubstrate 136. The ray apertures 134 may have a consistent diameter ormay have varying diameters.

The size and spatial arrangement of the ray apertures 134 may beselected based on the desired characteristics of the camera 106 to becalibrated and can be varied as desired. In one embodiment, the raygenerator 104 is an infrared (IR) light pass filter and the rayapertures are less than 0.2 mm in diameter and arranged in a 3×3 mmgrid. In this manner a light field display is generated when light fromthe emitting device is passed through the ray generator and the lightrays are angled based on the location of the ray apertures.

In embodiments where the ray generator 104 is active, the substrate 134forms an electronic display or other component and the ray apertures 136are pixels that are selectively modified to pass through or block light.For example, the substrate may be made up of pixels with liquid crystal,and when electrically stimulated, the liquid crystal may align to blockcertain wavelengths. In this manner, the ray apertures 136 aredynamically variable and may not be defined as actual holes in thedevice, but windows that allow wavelengths to pass through.

When the light-emitting device 103 is activated, the light generated bythe device 103 is transmitted through the spacing layer 130. The lightwaves that hit the blocking substrate 136 of the ray generator 104 areblocked and only light waves that align with the ray apertures 134 aretransmitted through the ray generator 104. In this manner, the raygenerator 104 generates a plurality of directional rays having a lowspread. The spread or solid angle of the emitted directional light isgenerally desirable to be reduced in order to enhance the calibrationprocess, but can be varied based on the device to be calibrated and thereconstruction algorithms. Some factors that influence the spreadincluding the aperture diameter, the thickness of the optical mask, thearea of the emitted light point (e.g., smaller pixels or larger pixels),diffraction of the light between the ray generator, light emitter,and/or optical device.

As noted above, in some embodiments the ray generator 104 may have ablocking substrate that selectively blocks certain wavelengths.Additionally, the spacing layer can be combined with one or more raygenerators to generate additional depth layers for the calibration.FIGS. 6 and 7 illustrate a second embodiment of the ray generator andspacing layer. With reference to FIGS. 6 and 7, in this embodiment, amultilayer mask 204 forms the ray generator, the multilayer maskincludes multiple wavelength specific ray generators 206 a, 206 b, 206 cand multiple spacing layers 208 a, 208 b, 208 c. In this example, eachof the wavelength-specific ray generators 206 a 206 b, 206 b include asubstrate 234 that selectively blocks one or more wavelengths, butallows other wavelengths to be transmitted through the substrate. Inthis configuration, the blocked wavelengths can only be transmittedthrough the ray apertures 236 defined in the substrate 234.

The wavelength specific ray generators 206 a, 206 b, 206 c are selectedto block different wavelengths. For example, the first ray generator 206a can be yellow and block blue light wavelengths 212 a 212 b; the secondray generator 206 b can be magenta and block green light wavelengths 214a, 214 b; and the third ray generator 206 c can be cyan and block redlight wavelengths 216 a, 216 b. In this example, the blue lightwavelengths 212 a, 212 b can be transmitted only through the rayapertures 236 in the first ray generator 206 a, but will pass throughthe substrates 234 of the other optical filters 206 b, 206 c (as well asany ray apertures in those substrates). As shown in FIG. 7, thisstructure results in additional rays that are generated at differentdepths, depending on the location of the specific light wavelength raygenerator 206 a, 206 b, 206 c. Other types of filter and colorcombinations can be used as well. Further, rather than using color (orin addition to color), additional ray generators may filter based onpolarization, e.g., polarized blocking. It should be noted that althoughthree wavelength ray generators are shown, fewer or more may be used.Additionally, although the ray generators are shown stacked inalignment, they may be offset from one another and/or used individuallyand the results combined together for the calibration.

With reference to FIG. 6, in this embodiment, the multilayer mask 204also includes multiple spacing layers 208 a, 208 b, 208 c. The spacinglayers 208 a, 208 b, 208 c are similar to the spacing layer 130 and areused to set a predetermined distance for the respective wavelengthspecific ray generator 206 a, 206 b, 206 c from the emitting device 103.The spacing layers 208 a, 208 b, 208 c allow the wavelength specificmasks, which may be positioned on top or of integrated with the spacinglayer, to be positioned at different depths from the emitting device103, which adds an additional depth component that increases accuracywith the calibration system 100.

The multilayer mask 204 generates a different perceived light volumethat can be captured by the optical device 106.

FIG. 8 illustrates the calibration example of FIG. 6 ready for use tocalibrate the optical device 106. With reference to FIG. 8, themultilayer ray generator 204 is assembled such that the variouswavelength specific ray generators 206 a, 206 b, 206 b are positioned ontop of their respective spacing layers 208 a, 208 b, 208 c, which are inturn positioned on top of the emitting device 103 and thelight-generating region. The optical device 106 is then aligned with themultilayer ray generator 204 and the emitting device 103 and capturesimages of the light rays that are generated by the emitting device 103and that extend through the ray generator 204.

FIG. 9 is a flow chart illustrating a method 300 for using thecalibration system 100 to calibrate the optical device 106. Withreference to FIGS. 1, 8, and 9, the method 300 begins with operation 302and structured light patterns are created. To generate the structuredlight patterns, the light-emitting device 103 is activated and givenspecific light patterns to emit. For example, binary structured lightpatterns such as dense binary structured light patterns, or otheremitted light that can represent or describe virtual points in space.The light patterns can be random, predetermined, or a combination. Thelight patterns can be selected such that they describe a specific point,random points, or the like. The ray generator 104, 204 generatesdirectional rays from the structured light patterns. The directionalrays are angled light rays that replicate the type of wavelengths thatcould be generated by an object positioned at different locationsrelative to the optical device 106. For example, a device that cangenerate rays of light that ca be tuned/adjusted to describe points thatare at various depths. The rays can represent one point, random points,predetermined points, or the like that may represent an objectpositioned at various locations from the optical device. In embodimentswhere the ray generator 104, 204 is an active mask, the differentdirectional rays may be generated at different stages where the raygenerator 104 varies characteristics of the ray apertures between orduring each projected light pattern.

Once the light patterns and directional rays have been generated, themethod 300 proceeds to operation 304 and the optical device 106 capturesimages of the light patterns. After the images are captured, the method300 proceeds to operation 306 and the computer 102 generatescorrespondences between the ray generator 104, 204, the emitting device103, and an image plane of the optical device 106. For example, thecomputer 102, and specifically, the processor element 108, determines acenter of projections on the image plane of the optical device 106, aswell as removes any outliers. In short, this operation is directed toassessing the center ray and can use detection algorithms or center ofgravity algorithms to determine the center ray. The device hardware, thelens hardware, the captured images, the aperture blocking effect of thelens can all be analyzed to detect the center directional ray.

Once the correspondence mapping is complete, the method 300 proceeds tooperation 308 and the processing element 108 determines the spatiallocations of the light rays are determined. For example, the processingelement 108 uses the ray aperture 136, 236 spacing (which is known),along with the size of the light-emitting region of the emitting device103, along with the spacing distance of the spacing layers 130 (if any)to determine the translation and rotation of the ray generators 104, 204by searching for rays that intersect as close as possible to a singlepoint.

Using the correspondences and the spatial locations, the method 300proceeds to operation 310 and the optical device 106 is calibrated. Inparticular, one or more calibration algorithm can be used to calibratethe optical device 106. In a first example, the locations of the rayapertures 136, 236 with respect to the emitting device 103 are known andthe two-dimensional (2D) correspondences can be described asthree-dimensional locations (3D) and a standard 2D to 3D calibrationmethod, such as direct linear transform (DLT) is used to determine thelens properties and optical device characteristics. It should be notedthat operations 308 and 310 can be done simultaneously and thecalibration algorithm and the spatial locations will be determinedduring the same process.

In a second example, a calibration method such as direct usage of thegenerated rays is used to estimate the lens properties of the opticaldevice 106.

In either example, optionally outlier tolerant and optimization methodscan be used to minimize the rear-projection error further. In short,substantially any calibration technique can be used as the relationshipbetween the rays captured or visible by the optical device 106 can becompared with the known directional rays that are transmitted to theoptical device 106 is known. This relationship illustrates the behaviorof the lens of the optical device 106, as well as inherentcharacteristics of the device itself. In other words, the mapping ofpixel positions as captured by the optical device. In other words, thecalibration assembly generates light rays that replicate 3D positions.

FIG. 10 illustrates a side elevation view of the calibration assembly103, 104 integrated into an attachment or accessory for the opticaldevice 106. With reference to FIG. 10, the calibration assembly 242 isan integrated device including the emitting device 103 and the raygenerator 104 connected together. The calibration assembly 242 can thenbe attached directly to a lens 240 of the optical device 106. In thisexample, the calibration assembly 242 can be screwed on or snap-fit ontothe outer end of the lens 240 similar to the attachment of a lens cap,additional lens, or the like. In this embodiment, the user error riskcan be substantially reduced as the calibration setup can be ensured tobe accurate.

The calibration system 100 and method 300 is highly repeatable as it iseasy for a user to set up, can be integrated into an accessory of theoptical device 106 (such as a lens cap or the like), and can becompleted in a small space. The method allows calibration of out offocus areas, as well as in-focus areas, and enables a small calibrationdesign that can be mounted directly to the optical device. Additionally,the calibration system and method help to un-distort images, enableaccurate projector calibration methods that require a calibrated camerafor projection mapping applications, as well as enhance sensitivity andaccuracy in motion tracking, image stitching, and 3D reconstruction.

The above specifications, examples, and data provide a completedescription of the structure and use of exemplary embodiments of theinvention as defined in the claims. Although various embodiments of thedisclosure have been described above with a certain degree ofparticularity, or with reference to one or more individual embodiments,those skilled in the art could make numerous alterations to thedisclosed embodiments without departing from the spirit or scope of theclaimed invention. Other embodiments are therefore contemplated. It isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as only illustrative ofparticular embodiments and not limiting. Changes in detail or structuremay be made without departing from the basic elements of the inventionas defined in the following claims.

What is claimed is:
 1. A system for calibrating an optical devicecomprising: a light ray generator for generating directional light raysin optical communication with the optical device, wherein the raygenerator separates light to generate a plurality of directional lightrays; and the directional light rays are captured by the optical device.2. The system of claim 1, further comprising a light emitting device inoptical communication with the ray generator, wherein the ray generatorseparates light emitted from the light emitting device to generate theplurality of directional rays.
 3. The system of claim 1, wherein the raygenerator is a holographic display that encodes information as afunction of both spatial position and angular direction.
 4. The systemof claim 1, wherein the ray generator comprises a plurality of rayapertures.
 5. The system of claim 4, wherein the ray apertures aredynamically generated.
 6. The system of claim 5, wherein the raygenerator comprises an active spatial light modulator.
 7. The system ofclaim 6, wherein the ray generator comprises a liquid crystal display.8. The system of claim 1, further comprising a computer in electroniccommunication with the optical device and the ray generator, wherein thecomputer analyzes the generated directional rays as compared to thedirectional rays captured by the optical device to determine one or morecalibration settings for the optical device.
 9. The system of claim 1,wherein the ray generator comprises: a first wavelength mask; a secondwavelength mask; and a third wavelength mask.
 10. The system of claim 9,wherein the first color mask, the second color mask, and the third colormask are arranged at different distances from the light-generatingdevice.
 11. The system of claim 1, wherein the light-emitting device isan electronic display screen.
 12. The system of claim 1, furthercomprising a spacing layer positioned between the light-emitting deviceand the ray generator.
 13. A method for calibrating an optical devicecomprising: generating by a light-generating device, a light pattern;separating by a ray generator the light pattern into a plurality oflight rays; capturing one or more images by the optical device of theplurality of light rays; and determining by a processing element one ormore lens properties of the optical device based on the light ray imagescaptured by the optical device.
 14. The method of claim 13, wherein theray generator comprises a plurality of ray apertures that segment thelight pattern into the plurality of light rays.
 15. The method of claim13, further comprising generating by the processing element a mappingbetween the plurality of light rays and the light pattern as generatedby the light-generating device.
 16. The method of claim 15, wherein thelight-generating device is an electronic display.
 17. The method ofclaim 13, wherein the ray generator comprises two or more wavelengthspecific ray generators having a blocking substrate that allowsselective wavelengths to pass therethrough.
 18. The method of claim 13,wherein the ray generator is active.
 19. A calibration assembly for usein calibrating a camera, comprising: an emitting device that generateslight wavelengths; and an optical mask in optical communication with theemitting device; wherein the optical mask separates the lightwavelengths emitted from the emitting device into one or moredirectional light rays.
 20. The calibration assembly of claim 19,wherein the optical mask is passive and includes a plurality ofpredefined ray apertures that separate the light wavelengths into theone or more directional light rays.
 21. The calibration assembly ofclaim 19, wherein the optical mask is active and includes a plurality ofpixels that are selectively modified to transmit or block the lightwavelengths to generate the one or more directional light rays.